// ThreadPool.h
#pragma once
#include <vector>
#include <queue>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <memory>
#include <stdexcept>

class ThreadPool
{
public:
    explicit ThreadPool(size_t);
    ~ThreadPool();

    template <class F, class... Args>
    auto enqueue(F &&f, Args &&...args)
        -> std::future<typename std::result_of<F(Args...)>::type>;

private:
    // 线程集合
    std::vector<std::thread> workers;
    // 任务队列
    std::queue<std::function<void()>> tasks;

    std::mutex queue_mutex;
    std::condition_variable condition;
    bool stop;
};

// 构造
inline ThreadPool::ThreadPool(size_t threads)
    : stop(false)
{
    for (size_t i = 0; i < threads; ++i)
        workers.emplace_back([this]
                             {
            for (;;) {
                std::function<void()> task;
                {
                    std::unique_lock<std::mutex> lock(this->queue_mutex);
                    this->condition.wait(lock, [this] {
                        return this->stop || !this->tasks.empty();
                    });
                    if (this->stop && this->tasks.empty())
                        return;
                    task = std::move(this->tasks.front());
                    this->tasks.pop();
                }
                task();
            } });
}

// 任务提交
template <class F, class... Args>
auto ThreadPool::enqueue(F &&f, Args &&...args)
    -> std::future<typename std::result_of<F(Args...)>::type>
{

    using return_type = typename std::result_of<F(Args...)>::type;

    auto task = std::make_shared<std::packaged_task<return_type()>>(
        std::bind(std::forward<F>(f), std::forward<Args>(args)...));

    std::future<return_type> res = task->get_future();
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        if (stop)
            throw std::runtime_error("enqueue on stopped ThreadPool");

        tasks.emplace([task]()
                      { (*task)(); });
    }
    condition.notify_one();
    return res;
}

// 析构
inline ThreadPool::~ThreadPool()
{
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        stop = true;
    }
    condition.notify_all();
    for (std::thread &worker : workers)
        worker.join();
}
